This invention relates to a magnetic recording medium for use in a magnetic disk apparatus and a method of manufacturing the same.
In recent years, a very high recording density has been required for a magnetic recording medium, such as a hard disk.
Generally, a magnetic recording medium such as a hard disk comprises an underlying layer, a magnetic layer, and a protection layer successively formed on a nonmagnetic substrate. Recording and reproducing operations are carried out by making a head slider with a magnetic head mounted thereon run in a floating state on the magnetic recording medium. In order to realize the magnetic recording medium which has a higher recording density, it is important to achieve, in addition to high coercive force of the magnetic layer, low floating height of the head slider, and high durability against CSS (Contact Start and Stop). Specifically, it is necessary to reduce the distance between the magnetic head and the magnetic layer during the recording and the reproducing operations by achieving the low floating height of the head slider so that the recording and the reproducing operations are carried out with high density. Such low floating height results in a drastic increase in physical and mechanical load applied to the magnetic head and magnetic recording medium when a sliding state and the floating state are repeatedly switched from one to another (CSS) at the time of start and stop of running of the head slider. Under the circumstances, it is also necessary to improve the durability of the magnetic head and the magnetic recording medium at the CSS (improvement in CSS durability). In addition, with the increase in recording density, the demand for suppression of noise upon the reproducing operation becomes more and more strict.
On the other hand, an aluminum alloy substrate has been traditionally used as the nonmagnetic substrate. Recently, a glass substrate is increasingly attracting attention. This is because that the glass is excellent in physical and chemical durability. This means that the glass substrate has a sufficient hardness to meet the recent trend of reduction in diameter and thickness of the hard disk. Furthermore, the glass has a nature such that its surface can be relatively easily formed with high accuracy. Thus, the glass is found to be suitable in realization of the higher recording density.
However, the above-described conventional method does not fully satisfy those severe demands in recent years. In particular, in order to carry out the recording and the reproducing operations with high density, it is essential to reduce medium noise and to increase an S/Nm ratio. For this purpose, a magnetic crystal grain size of the magnetic layer must be controlled. In the conventional method, however, restriction is imposed in controlling the magnetic crystal grain size of the magnetic layer to a more appropriate size.
It is therefore an object of the present invention to provide a magnetic recording medium which has an excellent magnetic characteristic.
It is another object of this invention to provide a method of manufacturing a magnetic recording medium, which can control a magnetic crystal grain size of a magnetic layer to a more appropriate size and which can therefore provide an excellent magnetic characteristic
According to an aspect of this invention, there is provided a magnetic recording medium comprising a nonmagnetic substrate of a crystallizable material and a lamina including at least a magnetic layer formed thereon. The nonmagnetic substrate has a surface specified by a predetermined crystal grain size while the magnetic layer has a magnetic crystal grain size dependent on the predetermined crystal grain size.
According to another aspect of this invention, there is also provided a method of manufacturing a magnetic recording medium which comprises a magnetic layer formed on a nonmagnetic substrate of a crystallizable material. The method comprises the steps of selecting the nonmagnetic substrate which has a surface of a predetermined crystal grain size, to thereby control a magnetic crystal grain size of the magnetic layer.